Lithographic process having sub-wavelength resolution

ABSTRACT

A lithographic process for making an article such as a semiconductor device or a lithographic mask is disclosed. In the process, articles are fabricated by a sequence of steps in which materials are deposited on a substrate and patterned. These patterned layers are used to form devices on the semiconductor substrate. The desired pattern is formed by introducing an image of a first pattern in a layer of energy sensitive material. The image is then developed to form a first pattern. A layer of energy sensitive material is then formed over the first pattern. An image of a second pattern is then formed in the layer of energy sensitive material formed over the first pattern. The second pattern is then developed. The desired pattern is then developed from the first pattern and the second pattern.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention is directed to lithographic processes for deviceand mask fabrication and, in particular, to resolution enhancementtechniques for such processes.

2. Art Background

In lithographic processes for device fabrication, radiation is typicallyprojected onto a patterned mask (also referred to as a reticle) and theradiation transmitted through the mask is further transmitted onto anenergy sensitive material formed on a substrate. Transmitting theradiation through a patterned mask patterns the radiation itself and animage of the pattern is introduced into the energy sensitive materialwhen the energy sensitive resist material is exposed to the patternedradiation. The image is then developed in the energy sensitive resistmaterial and transferred into the underlying substrate. An integratedcircuit device is fabricated using a series of such exposures to patterndifferent layers of material formed on a semiconductor substrate.

An integrated circuit device consists of a very large number ofindividual devices and interconnections therefore. Configuration anddimensions vary among the individual devices. The pattern density, (i.e.the number of pattern features per unit area of the pattern) alsovaries. The patterns that define integrated circuit devices aretherefore extremely complex and non-uniform.

As the complexity and density of the patterns increase, so does the needto increase the accuracy of the lithographic tools that are used tocreate the patterns. The accuracy of lithographic tools is described interms of pattern resolution. The better the resolution, the closer thecorrespondence between the mask patterns and the pattern that is createdby the tool. A number of techniques have been used to enhance thepattern resolution provided by lithographic tools. The most prevalenttechnique is the use of shorter wavelength radiation. However, thistechnique is no longer viable when exposure wavelengths are in the deepultraviolet (e.g., 248 nm, 193 nm and 157 nm) range. Using wavelengthsbelow 193 nm to improve resolution is presently not economically andtechnologically feasible because the materials used for lenses inoptical lithography cameras absorb this shorter wavelength radiation.

Resolution enhancement techniques (RET) other than simply using shorterwavelength radiation have been proposed. These techniques use exoticillumination from the condenser (e.g. quadrupole illumination), pupilfilters, phase masks, optical proximity correction, and combinations ofthese techniques to obtain greater resolution from an existing camera.However, such techniques typically improve resolution only for some ofthe individual features of a pattern. The features for which resolutionis improved are identified as the critical features. The resolution ofmany other features is either not improved or actually degraded by suchresolution enhancement techniques. Thus, current RETs require acompromise between resolution enhancement for the critical features andresolution degradation for the non-critical features. Such compromisesusually require sub-optimal illumination of the critical features inorder to avoid significant degradation in the illumination of thenon-critical features.

Resolution enhancement techniques have been proposed to customize maskfeature illumination in projection lithography for the various differentfeatures in the mask. One such technique is described in Matsumoto, K.,et al., “Innovative Image Formation: Coherency Controlled Imaging,”SPIE, Vol. 2197, p. 844 (1994). That technique employs an additionalmask and additional lens to customize the radiation incident on eachfeature of the mask. A similar system is described in Kamon, K.,“Proposal of a Next-Generation Super Resolution Technique,” Jpn. J.Appl. Phys., Vol. 33, Part 1, No. 12B, p. 6848 (1994).

In the resolution enhancement techniques described in Matsumoto et al.and Kamon et al., the first mask has features that are identical to thefeatures on the second mask. The features on the first mask diffract theradiation incident on the mask, and the diffracted radiation illuminatesthe identical feature on a second mask. For example, radiationtransmitted through a grating pattern on the first mask is projectedonto an identical grating pattern on the second mask. Similarly,radiation transmitted through an isolated line on the first mask isprojected onto an identical isolated line on the second mask. When thediffracted energy from the first mask illuminates the identical featureon the second mask, the resulting image is often superior to an imageobtained from quadrupole illumination of the pattern. Therefore, thisresolution enhancement technique provides an improvement in aerial imagecontrast (i.e. the image in the focus plane of the projection lens) overconventional off-axis illumination using the quadrupole system.

The above-described resolution enhancement technique provides customizedillumination for more features than quadrupole illumination. However,the above-described technique does not improve the resolution of allfeatures in the pattern. Furthermore, the two-mask system is costly andcomplex. Specifically, the system requires two precisely patterned masksinstead of one. The corresponding features on the first and second masksmust match precisely. The alignment of the first and second masks isalso critical. Furthermore, the technique is limited because thefeatures on the first mask are illuminated uniformly. Thus, the problemsassociated with non-customized illumination of a patterned mask are noteliminated by this system, but simply stepped further back into theoptics of the system. Therefore, resolution enhancement techniques thatimprove the resolution of all features and are cheaper and easier toimplement are sought.

SUMMARY OF THE INVENTION

The present invention is directed to a lithographic process withsub-wavelength resolution. The lithographic process is used for devicefabrication or for mask fabrication. In the present invention, an imageof a pattern is introduced into an energy sensitive resist material byprojecting radiation through a first mask feature which defines an imageof a first pattern. The radiation is light of a particular wavelength(e.g. 248 nm, 193 nm, etc.). Radiation also includes electron beam orion beam radiation. That first pattern is then developed and, in certainembodiments, transferred into the underlying substrate. This firstpattern is referred to as an intermediate feature. The intermediatefeature has dimensions that are typically, greater than or approximatelyequal to the wavelength of the radiation that is used to transfer theimage of the first mask feature into the energy sensitive resistmaterial. It is advantageous for the intermediate feature to havedimensions greater than or equal to the wavelength of the exposingradiation because the images from which the features are created areeasier to resolve than images with sub-wavelength size dimensions. Also,creating images of features having dimensions greater than or equal tothe wavelength of exposing radiation requires less proximity effectcorrection and suffers from fewer adverse diffraction effects comparedto creating images of features with sub-wavelength dimensions. Adversediffraction effects include a loss of contrast, a loss of intensity,adverse proximity effects, etc.

A layer of energy sensitive material is then formed over substratehaving the intermediate feature. An image of a pattern is thenintroduced into the energy sensitive resist material by projectingradiation through a second mask feature which defines a second image.The radiation used for the second exposure does not have to have thesame wavelength as the radiation used for the first exposure. Thissecond image is developed into a second pattern, which is referred to asa second intermediate feature. The second intermediate feature hasdimensions that are greater than or approximately equal to thewavelength of the radiation that is used to introduce the second imageinto the resist material. The advantages that derive from formingintermediate features with dimensions larger than or equal to thewavelength of the exposing radiation are as previously described. Thefirst mask feature and the second mask feature cooperate to define adesired pattern feature. The desired pattern feature is defined by thefirst intermediate feature created from the first mask feature and thesecond intermediate feature created from the second mask feature. In oneembodiment, the first intermediate feature and the second intermediatefeature define the pattern feature, which is transferred into theunderlying substrate. In another embodiment, the pattern feature isdefined by the overlap between the first intermediate feature and thesecond intermediate feature. In this embodiment, the pattern feature isformed by selectively removing the non-overlapping portions of the firstintermediate feature and the second intermediate feature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of one process sequence of thepresent invention.

FIG. 2 is a schematic illustration of a second process sequence of thepresent invention.

FIG. 3 is a schematic illustration of a third process sequence of thepresent invention.

FIG. 4 illustrates a first mask pattern, a second mask pattern, and afeature formed therefrom.

FIG. 5 illustrates two mask patterns and a feature formed therefrom.

FIG. 6 illustrates two square mask patterns and a roughly ellipticalcontact hole pattern formed therefrom.

DETAILED DESCRIPTION

Referring to FIG. 1, radiation 20 is patterned by mask 10 in step 1. Thepatterned radiation introduces an image of the mask 10 into a layer ofenergy-sensitive photoresist 25. In step 2, the image in layer 25 isdeveloped to form a photoresist mask. In step 3, the photoresist maskpattern is then etched into the underlying layer of hard mask material30, formed on a silicon substrate 35. Conventional hard mask materials,such as oxidized silicon, silicon nitride and spin-on glass, arecontemplated as suitable. A layer of energy-sensitive photoresist 36 isthen formed over the patterned layer of hard mask material. In step 4,an image of mask 40 is then introduced into the photoresist 36. Theimage of mask 40 overlaps with the patterned layer of hard mask material30. In step 5, the image is then developed to obtain a patterned resistlayer 36. The resulting structure has a first patterned hard mask 30 anda second patterned resist layer 36 formed on the substrate 35. These twopatterned layers together define a feature 45, which has a dimensionsmaller than the wavelength of the exposing radiation. In step 6, thepatterned layers 30 and 36 are used to transfer the feature 45 into theunderlying substrate 35. Conventional etch expedients are contemplatedas suitable for this purpose. In step 7, the patterned layers 30 and 36are removed from the substrate 35 with feature 45 etched therein.

Referring to FIG. 2, radiation 101 is projected through a mask 100 instep 1. The radiation introduces an image of a pattern in energysensitive resist layer 102, which is formed over a layer of hard maskmaterial 103, which is formed on a silicon substrate 104. Since, in thisprocess sequence, the feature is formed in the hard mask material layer,the hard mask material is either a dielectric material (e.g. oxidizedsilicon, silicon nitride) or a metal. It is advantageous if the hardmask material is a dielectric material because of the contaminationissues associated with the use of metals as masking layers. In step 2,the pattern is then developed in energy sensitive resist layer 102. Instep 3, the pattern is transferred from resist layer 102 and into thelayer of hard mask material 103. A layer of energy sensitive material isthen formed on the resulting structure. In step 4, radiation 10 isprojected through mask 105 and the patterned radiation introduces animage of a pattern in energy sensitive resist layer 106. In step 5, thepattern is then developed in energy sensitive resist layer 106. Notethat a portion of the developed resist layer 106 overlies a portion ofthe patterned hard mask 103. This region of overlap 107 is the desiredpattern. In step 6, the portion of the patterned hard mask layer that isnot covered by the developed resist layer 106 is removed. In step 7, thedeveloped resist layer 106 is removed and the feature 108 that resultsis the portion of the patterned hard mask layer that was in the regionof overlap 107. Again, although the dimensions of the patterns developedin steps 3 and 5 are greater than the wavelength of the exposingradiation, the dimensions of the feature 108 are less than thewavelength of the exposing radiation. It is in this manner that theprocess of the present invention is used to fabricate features that havea dimension smaller than the wavelength of the exposing radiation.

Referring to FIG. 3, a negative resist material is used in the processof the present invention. When a negative resist is patternwise exposedto radiation and the image is developed, the exposed portion of theresist remains and the unexposed portion of the resist is developed out.In step 1, radiation 201 is projected through a mask 200. The radiationintroduces an image of a pattern in energy sensitive resist layer 202,which is formed over a second layer of 203, which is formed on a siliconsubstrate 204. The second layer 203 is typically a dielectric layer. Inthis embodiment, layer 203 does not function as a hard mask. Therefore,the criteria for selecting the specific material for layer 203 aredetermined by the device being fabricated. In step 2, the pattern isthen developed in energy sensitive resist layer 202. In step 3, a layerof energy sensitive material 206 is then formed on the resultingstructure. In step 4, radiation 210 is projected through mask 205 andthe patterned radiation introduces an image of a pattern in energysensitive resist layer 206. In step 5, the pattern is then developed inenergy sensitive resist layer 206. The solvent that is used to developthe pattern in step 5 selectively dissolves the unexposed portion oflayer 206 does not dissolve the underlying patterned resist layer 202.The choice of a particular solvent for the selective development ofresist layer 206 that will not dissolve underlying patterned resistlayer 202 is readily made by one skilled in the art. Specifically, if afirst solvent is selected to develop the pattern 206, the polarity ofpatterned layer 202 will have a polarity such that it is not soluble inthe first solvent. One skilled in the art is aware of suitable resistmaterials and suitable solvents for this embodiment of the presentinvention. A description of solvents for selective development andoptical, dual layer resists is found in Moreau, W. M., et al.,Semiconductor Lithography Principles, Practices, and Materials, p. 586(1987) which is incorporated by reference herein. Note that thedeveloped resist layers 202 and 206 define a space 207. This space 207is the desired feature, which is transferred into the second layer 203in step 6. In step 7, the developed resist layers 202 and 206 areremoved. Again, although the dimensions of the patterns developed insteps 3 and 5 are greater than the wavelength of the exposing radiation,the dimensions of the feature 207 are less than the wavelength of theexposing radiation. It is in this manner that the process of the presentinvention is used to fabricate features that have a dimension smallerthan the wavelength of the exposing radiation.

One skilled in the art will appreciate that many different patterns arepossible using the overlapping patterns of the present invention. Oneexample of a pattern is illustrated in FIG. 4. In FIG. 4, a firstpattern 300 is developed in a resist and transferred into a layer ofsilicon dioxide as described in steps 1-3 of FIG. 1. The pattern 300 isobtained by projecting radiation through a first mask (not shown) thatdefines a series of lines and spaces. The radiation projected throughthe mask defines an image of the mask pattern in the energy sensitiveresist. That image is then developed using a developer to selectivelyremove the portion of the resist that was exposed to radiation. Thedeveloped pattern in the energy sensitive resist is then transferredinto the underlying layer of oxidized silicon 301. The result is a firstpattern that is a series of lines 301 on a silicon substrate. In the topview of the pattern illustrated in FIG. 4, the regions 301 are theregions of silicon oxide and the regions 302 are the substrate surface.

A layer of energy sensitive resist 309 is formed over the pattern. Animage of a pattern is delineated in the energy sensitive resist. Thatimage 310 is of a series of lines and spaces defined by regions 311,which are exposed to radiation, and regions 312, which are not exposedto radiation. That image is introduced into the energy sensitive resistby projecting radiation through a mask that defines a series of linesand spaces and onto the layer of energy sensitive resist. Therelationship between the image 310 in the energy sensitive resist layer309 and the underlying pattern 300 is illustrated by dashed lines 305.That relationship is such that the edge of exposed region 311 extendsbeyond edge of the underlying line 301. The distance 304 that the edgeof exposed region 311 extends beyond the edge of underlying line 301 isthe width of the desired feature. The width of the desired feature isless than the wavelength of the exposing radiation. In one example, thewavelength of the exposing radiation is 248 nm and the distance 304 is50 nm.

After the image 310 is defined in the energy sensitive resist 309, thepattern is developed by removing the exposed portion 311 of the energysensitive resist material. The dashed lines 305 indicate the edge of theunderlying lines 301. The distance 304 is the portion of the underlyingsubstrate that is exposed between the remaining portion of layer 309 andthe oxidized silicon lines 301. The remaining portion of layer 309 andthe lines of oxidized silicon 301 serve as an etch mask for transferringa trench having width 304 into the underlying substrate. The oxidizedsilicon lines 301 and the remaining portion of resist layer 309 are thenstripped from the surface of the substrate. A top view of the resultingpattern 320, i.e. a substrate 314 with trenches 315 formed therein isprovided in FIG. 4. The oxidized silicon lines 301 and the differencebetween the edge of the exposed portion 311 in the overlying layer ofphotoresist and the edge of the underlying line 311. The desired pattern320, is the region defined by the distance between the edge of the firstfeatures 301 from the first mask and the edge of the resist features 311in the second pattern 310.

Another example of a pattern formed using the process of the presentinvention is illustrated in FIG. 5. In FIG. 5, a first pattern 400 isdeveloped in a resist and transferred into a layer of oxidized siliconas described in steps 1-3 of FIG. 2. The pattern 400 is obtained byprojecting radiation through a first mask (not shown) that defines aring. The radiation projected through the mask defines an image of themask pattern in the energy sensitive resist. That image is thendeveloped using a developer to selectively remove the portion of theresist that was exposed to radiation. The developed pattern in theenergy sensitive resist is then transferred into the underlying layer ofoxidized silicon 401. The result is a first pattern 400 that is a ringof oxidized silicon 401 on a silicon substrate 402. In the top view ofthe pattern illustrated in FIG. 5, the region 401 is the region ofsilicon oxide and the regions 402 are the exposed substrate surface.

A layer of energy sensitive resist 409 is formed over the ring pattern400. An image of a pattern is delineated in the energy sensitive resist.That image 410 is of a circle defined by region 411, which is notexposed to radiation, and region 412, which is exposed to radiation.That image is introduced into the energy sensitive resist by projectingradiation through a mask that defines a circle and onto the layer ofenergy sensitive resist. The relationship between the image 410 in theenergy sensitive resist layer 409 and the underlying pattern 400 isillustrated by dashed lines 405. That relationship is such that theinner edge of the ring is within and concentric with the unexposedcircular region 412. The distance 404 between the edge of the inner ringof the pattern 400 and the outer edge of the unexposed, circular region411 is the width of the desired feature. The width of the desiredfeature is less than the wavelength of the exposing radiation. In oneexample, the wavelength of the exposing radiation is 248 nm and thedistance 404 is 50 nm.

After the image 410 is defined in the energy sensitive resist 409, thepattern is developed by removing the exposed portion 411 of the energysensitive resist material. The dashed lines 405 indicate the edges ofthe underlying ring pattern 400. The distance 404 is the portion of theunderlying oxidized silicon ring that is covered by the unexposedportion of the energy sensitive resist material 411 after the exposedportion of the energy sensitive resist material 412, along with theportion of the oxidized silicon ring underlying it, is removed.Referring to step 6 of FIG. 2, the remaining portion of the oxidizedsilicon ring corresponds, in side view, to the oxidized silicon 107. Theremaining portion of energy sensitive resist layer 409 is then removed.The resulting pattern 420 is a ring of oxidized silicon 415 formed on asilicon substrate 414.

Contact holes with a dimension smaller than the wavelength of theexposing radiation are also produced using the process of the presentinvention. Contact holes are produced by creating a first intermediatepattern that is a rectangle or square. As one skilled in the art isaware, the pattern that results from an image with square corners hascorners that are somewhat rounded. After the first pattern with roundedcorners is developed, a layer of energy sensitive material is formedover the pattern and the image of a second square or rectangle is formedtherein. The image of the second square or rectangle is positioned suchthat one corner overlaps one corner of the underlying pattern withrounded corners. The image of the second square or rectangle is thendeveloped and it, too, has rounded corners. The pattern defined by theoverlapping portion of the first pattern and the second pattern is thendeveloped. Since this pattern is created from overlapping patterns ofrounded corners, the resulting pattern is defined by two roundedcorners. Consequently, the resulting pattern approximates an ellipse ora circle. The resulting pattern 500, as defined by overlapping cornersof rectangles 501 and 502, is illustrated in FIG. 6. The roughlyelliptical pattern, 500, is defined by dashed lines.

EXAMPLE 1

A set of four binary reticles (masks) was obtained from Dupont PhotomaskInc. The masks were made using a laser tool and defined numerousdifferent patterns. Two examples of the numerous patterns are depictedin FIG. 4 and FIG. 5. The reticle address space (i.e. the size of theaddressable units (pixels) in the mask) was 40 nm. The smallest featureson the mask had a dimension of 1 μm. The mask had a registrationspecification of 60 nm. The patterns in two of the four masks are thenegative of the patterns in the other two masks so that differentcombinations of dark-field and bright field illumination and positiveand negative photoresists were used. An XLS 7800 lithographic exposuretool was used for exposure. Ultratech Stepper, Inc manufactured thetool. The tool had a magnification of 4×, used an exposure wavelength of248 nm, had a σ coherence factor of 0.74 and had a NA (numericalaperture) of 0.53. The positive energy sensitive resist (photoresisthereinafter) used for these examples was UV6™ which was obtained fromthe Shipley Company of Marlborough, Mass. The negative photoresist usedfor these examples was UV2™ which was also obtained from the ShipleyCompany.

Numerous mask patterns were used to create a variety of structureshaving a variety of configurations. One such mask pattern is the lineand space pattern used to create the pattern 300 in FIG. 4. The linesand spaces were 0.25 μm wide. Another example of two masks thatcooperate to provide a desired pattern are the masks used to create ringpattern 400 and circle pattern 410. The pattern that results from theuse of the two masks in the process described in FIG. 2 and theaccompanying text is the pattern 420.

A 1000-angstrom thick layer of oxidized silicon was deposited on siliconwafers. A layer of UV6™ energy sensitive resist was spin-coated over thelayer of oxidized silicon. The spin-coated resist had a thickness of 680nm. The photoresist was then pre-baked at 138° C. for sixty seconds.

Following the sequence described in FIG. 2, the positive photoresist waspatternwise exposed to radiation using the previously describedline-and-space mask. The lines and spaces in the image delineated in thephotoresist had an individual width of 0.25 μm and a length of 1 μm. Thedose of radiation introduced into the photoresist was 40 mJ/cm². Thepattern was then subjected to a post-exposure bake at a temperature of130° C. for 90 seconds. The pattern was developed using a conventionaldeveloper, tetramethylammonium hydroxide (TMAH) in combination withdeveloper 262 (obtained from the Olin Microelectronics, Inc.). Thedeveloper was applied as a stream onto the wafer for about 15 seconds.After about 45 seconds, the wafer was rinsed and dried. The pattern wasthen transferred into the underlying layer of silicon oxide using anApplied Materials' 5000 Magnetron etch.

The pattern was etched at 33° C. using 65 sccm (standard cubiccentimeter per minute) of trifluoromethane and 3 sccm ofhexafluorosilane for 25 seconds. The pattern was then further etchedusing a mixture of 30 sccm trifluoromethane, 60 sccm argon and 4 sccmtetrafluoromethane for twenty seconds. The resist remaining after theetch was stripped in an oxygen plasma at 250° C. for ninety seconds.

A layer of photoresist (the previously described UV6™ positive resist)was then applied over the resulting structure. The photoresist had athickness of 700 nm. The resist thickness was selected to ensure thatportions of the substrate underlying the unexposed resist were notexposed to the etchant. The thickness was determined based upon thedifference between the etch rate of the exposed and unexposed resist,and the etch rate of the unexposed resist. The photoresist was thenexposed to radiation by projecting a 40 mJ/cm² dose of radiation usingthe mask that provides the pattern 310 illustrated in FIG. 4.Registration of the image with the previous pattern was accomplished byusing standard alignment techniques. In this example, the mask patternused for the second exposure is the same as the mask pattern for thefirst exposure. However, the second exposure was offset relative to theunderlying pattern that was produces from the first exposure. The offsetdistance corresponded to the desired feature size. In this example,numerous patterns were fabricated. Different offsets were used to makedifferent patterns. The offset of the image produced from the secondexposure relative to the first pattern was varied from 0.05 μm to about0.2 μm.

The pattern was then developed as previously described in this Example.The resulting structure is a patterned photoresist layer and a patternedsilicon dioxide layer on the substrate. As illustrated in step 5 of FIG.1, the desired pattern is the portion of the substrate surface that isnot covered by either the oxidized silicon mask or the photoresist mask.The pattern is transferred into the underlying substrate by selectivelyetching the exposed portion of the substrate surface, wherein thepattern oxidized silicon and remaining photoresist function as an etchmask. The etch expedients used for this pattern transfer step werehexafluoroethane (90 sccm) and oxygen plasma (10 sccm) for twenty-fiveseconds at 33° C. The remaining photoresist and oxidized silicon werestripped from the substrate surface using expedients well known to oneskilled in the art.

The resulting patterns were a series of lines and spaces. For allpatterns, the line length was 1 μm. The width of the lines varied from0.05 μm to 0.2 μm for the patterns. As previously noted, the linewidthwas determined by the offset distance between the pattern that resultedfrom the first exposure and the image (and resulting developed pattern)that was obtained from the second exposure.

In the process of the present invention, the second mask must beregistered with the first pattern from the first exposure in order toobtain a correspondence between the position of the first pattern andthe position of the second pattern. Positional correspondence isrequired in order to obtain the desire pattern. The registration error(i.e. the difference between a desired position and an actual position)is less than about 30 nm. In the wafer coordinate system, theintersection of the x-axis and y-axis is approximately located in thecenter of the wafer. Thus, in the wafer coordinate system, the wafer isdivided into four quadrants. The mean registration error across asix-inch wafer was −28 nm (with a 3σ_(x)=96 nm) along the x-axis and 6nm (with a 3σ_(y)=89 nm) along the y-axis. Typically, current steppersprint with a mean-plus-3σ of 40 nm.

The present invention has been described in terms of specific examples.These examples have been provided to illustrate certain embodiments ofthe claimed invention. For example, the present invention has beendescribed in terms of a first exposure (using a first mask pattern) anda second exposure (using a second mask pattern). One skilled in the artwill appreciate that the present invention will be practiced using twoor more exposures. Also, the process of the present inventions is usedto form any pattern. This is in addition to the specific patterns ofline and spaces, rings and holes described herein by way of example.Consequently the examples are provided to illustrate the claimedinvention and should not be construed to limit the present invention,except in a manner consistent with the appended claims.

What is claimed is:
 1. A lithographic process for fabricating an articlecomprising: directing radiation of a certain wavelength onto a maskhaving a first pattern therein; projecting an image of the first patterninto a layer of energy sensitive material formed on a substrate;developing the image to form the first pattern in the energy sensitivematerial; forming a layer of energy sensitive resist material over thefirst pattern; directing radiation of a certain wavelength onto a maskhaving a second pattern therein wherein the wavelength is either thesame or different than the wavelength of the radiation directed onto themask having the first pattern; projecting an image of the second patterninto the layer of energy sensitive resist material wherein the image isaligned with the underlying first pattern so that the first pattern andthe second pattern cooperate to define a desired pattern; developing theimage to form the second pattern in the energy sensitive material; anddeveloping the desired pattern from the first and second pattern,wherein the desired pattern has a dimension that is smaller than atleast one of the wavelengths of radiation.
 2. The process of claim 1wherein the article is a semiconductor device.
 3. The process of claim 2wherein the substrate is a semiconductor substrate on which is formed alayer of material wherein the material is selected from the groupconsisting of a hard mask material, a dielectric material and a metal.4. The process of claim 3 wherein the energy sensitive material is apositive energy sensitive material.
 5. The process of claim 4 furthercomprising transferring the developed first pattern into the layer ofmaterial formed on the semiconductor substrate.
 6. The process of claim5 wherein the first and second patterns have a thickness with edgesorthogonal to the substrate surface and wherein the image of the secondpattern is aligned with the first pattern such that there is a distancebetween an edge of the first pattern and an edge of the second pattern,wherein the desired pattern is defined by the distance and the distanceis less than the wavelength of the exposing radiation.
 7. The process ofclaim 6 wherein a portion of the underlying semiconductor substrate isexposed between the edge of the first pattern and the edge of the secondpattern and further comprising transferring the desired pattern into theunderlying substrate.
 8. The process of claim 6 wherein a portion of thesecond pattern extends over a portion of the first pattern and furthercomprising transferring the desired pattern into the layer of materialformed on the semiconductor substrate.
 9. The process of claim 3 whereinthe energy sensitive material is a negative energy sensitive material.10. The process of claim 9 wherein the first and second patterns have athickness with edges orthogonal to the substrate surface and wherein theimage of the second pattern is aligned with the first pattern such thatthere is a distance between an edge of the first pattern and the edge ofthe second pattern, wherein the desired pattern is defined by thedistance and the distance is less than the wavelength of the exposingradiation.
 11. The process of claim 10 wherein a portion of the layer ofmaterial formed on the substrate is exposed between the edge of thefirst pattern and the edge of the second pattern and further comprisingtransferring the desired pattern into the layer of material formed onthe substrate.
 12. The process of claim 1 wherein the article is alithographic mask.